A hub is part of the mechanical interface between a wheel and the chassis of a vehicle. The hub may be mounted to the rim of a wheel, either directly in the rim or connected to the rim by spokes or the like. In some examples, the hub is further provided with one or more bearings that are mounted in the hub such that the bearing outer ring is fixed to the hub. The inner ring of the bearing is mounted to an axle of some kind. The axle is used to mount the wheel to a vehicle. In this way, the wheel will be able to rotate in relation to the vehicle.
A hub may comprise a bearing unit, where the bearing unit comprises rolling element bearings and an outer and inner sleeve of some kind. A hub unit may comprise a bearing unit and a shaft. Such a bearing unit or a hub unit is easier to mount in machinery or on a vehicle and is also more cost-effective to use, since it comes pre-assembled and pre-greased. It will also save maintenance cost by allowing the complete bearing unit or hub unit to be replaced as one part in case of failure.
When a bearing unit is used on a vehicle, the bearing unit is exposed to different loads. It is of advantage to be able to measure the loads imposed on a bearing unit, since these loads will be measured on the unsprung mass of the vehicle. The knowledge of the forces imposed on the hub can be used for several different vehicle functions, both to improve the comfort and safety for the user. Load monitoring is also useful for the prediction of maintenance intervals.
It is possible to measure the loads imposed on a hub in different ways. One way is to use accelerometers measuring in one or more directions. Another way is to use strain sensors positioned in the hub, either on the inner or outer races of the bearings or on a non-rotating part of the hub assembly. U.S. Pat. No. 4,168,160, JP2007171102, WO 06122269 and U.S. Pat. No. 6,490,935 describe different bearing assemblies with integrated force measuring capabilities.
WO 07043885 describes a bearing and shaft assembly, in which strain sensors are provided on an inner tubular element, which is mounted between the shaft and the bearings. This bearing and shaft assembly is especially adapted for the use on a motorcycle.
Furthermore, in U.S. Pat. No. 7,240,570, a load sensing bearing is suggested in which the bearing outer ring is supported within a flange assembly, whereby the flange assembly is used to mount the bearing to an application structure. The flange assembly comprises anisotropic spring regions and is instrumented with load cells for measuring forces and moments acting on the bearing.
There is still room for improvement, however, in terms of realizing a compact and lightweight bearing unit that is capable of accurately measuring axial forces, radial forces and moments acting on the bearing. There is also a need for an improved load measuring device that enables the realization of such a bearing unit.